FullForm
,
Echo
,
PrettyForm
,
EvalFormula
,
TeXForm
,
CForm
,
Write
,
WriteString
,
Space
,
NewLine
,
FromFile
,
FromString
,
ToFile
,
ToString
,
Read
,
LispRead
,
ReadToken
,
Load
,
Use
,
DefLoad
,
FindFile
,
PatchLoad
,
Nl
,
V
.
Input/Output
This chapter contains commands to use for input and output. All output
commands write to the same destination stream, called the "current
output". This is initially the screen, but may be
redirected by some commands. Similarly, most input commands
read from the "current input" stream, which can also be redirected. The
exception to this rule are the commands for reading script files,
which simply read a specified file.
FullForm
|
Print an expression in LISP-format |
Echo
|
High-level printing routine |
PrettyForm
|
Print an expression nicely with ASCII art |
EvalFormula
|
Print an evaluation nicely with ASCII art |
TeXForm
|
export expressions to LaTeX |
CForm
|
export expression to C code |
Write
|
Low-level printing routine |
WriteString
|
Low-level printing routine for strings |
Space
|
Print one or more spaces |
NewLine
|
Print one or more newline characters |
FromFile
|
Connect current input to a file |
FromString
|
Connect current input to a string |
ToFile
|
Connect current output to a file |
ToString
|
Connect current output to a string |
Read
|
Read an expression from current input |
LispRead
|
Read an expression in LISP-syntax |
ReadToken
|
Read an token from current input |
Load
|
Evaluate all expressions in a file |
Use
|
Load a file, but not twice |
DefLoad
|
Load a .def file |
FindFile
|
Find a file in the current path |
PatchLoad
|
Execute commands between <? and ?> in file |
Nl
|
A newline character |
V
|
Verbose mode output |
FullForm -- Print an expression in LISP-format
Internal function
Calling format:
Parameters:
expr - The expression to be printed in LISP-format
Description:
Evaluates "expr", and prints it in LISP-format on the current
output. It is followed by a newline. The evaluated expression is also
returned.
This can be useful if you want to study the internal representation of
a certain expression.
Examples:
In> FullForm(a+b+c);
(+ (+ a b )c )
Out> a+b+c;
In> FullForm(2*I*b^2);
(* (Complex 0 2 )(^ b 2 ))
Out> Complex(0,2)*b^2;
|
The first example shows how the expression a+b+c is
internally represented. In the second example, 2*I is
first evaluated to Complex(0,2) before the expression
is printed.
See also:
LispRead
,
Listify
,
Unlist
.
Echo -- High-level printing routine
Standard library
Calling format:
Parameters:
item - the item to be printed
list - a list of items to be printed
Description:
If passed a single item, Echo will evaluate it and print it to the
current output, followed by a newline. If "item" is a string, it is
printed without quotation marks.
If the second calling sequence is used, Echo will print all the
entries in the list subsequently to the current output, followed by a
newline. Any strings in the list are printed without quotation
marks. All other entries are followed by a space.
Echo always returns True.
Examples:
In> Echo(5+3);
8
Out> True;
In> Echo({"The square of two is ", 2*2});
The square of two is 4
Out> True;
|
Note that one must use the second calling format if one wishes to
print a list:
In> Echo({a,b,c});
a b c
Out> True;
In> Echo({{a,b,c}});
{a,b,c}
Out> True;
|
See also:
PrettyForm
,
Write
,
WriteString
.
PrettyForm -- Print an expression nicely with ASCII art
Standard library
Calling format:
Parameters:
expr - an expression
Description:
PrettyForm renders an expression in a nicer way, using ascii art.
This is generally useful when the result of a calculation is more
complex than a simple number.
Examples:
In> Taylor(x,0,9)Sin(x)
Out> x-x^3/6+x^5/120-x^7/5040+x^9/362880;
In> PrettyForm(%)
3 5 7 9
x x x x
x - -- + --- - ---- + ------
6 120 5040 362880
Out> True;
|
See also:
EvalFormula
,
PrettyPrinter
.
EvalFormula -- Print an evaluation nicely with ASCII art
Standard library
Calling format:
Parameters:
expr - an expression
Description:
Show an evaluation in a nice way, using PrettyPrinter
to show 'input = output'.
Examples:
In> EvalFormula(Taylor(x,0,7)Sin(x))
3 5
x x
Taylor( x , 0 , 5 , Sin( x ) ) = x - -- + ---
6 120
Out> True
|
See also:
PrettyForm
.
TeXForm -- export expressions to LaTeX
Standard library
Calling format:
Parameters:
expr -- an expression to be exported
Description:
TeXForm() returns a string containing a LaTeX representation of the Yacas expression expr. Currently the exporter handles most expression types but not all.
Example:
In> TeXForm(Sin(a1)+2*Cos(b1))
Out> "$\sin a_{1} + 2 \cos b_{1}$";
|
See also:
PrettyForm
,
CForm
,
ShowPS
.
CForm -- export expression to C code
Standard library
Calling format:
Parameters:
expr -- expression to be exported
Description:
CForm() returns a string containing a C/C++ code implementing the Yacas expression expr. Currently the exporter handles most expression types but not all.
Example:
In> CForm(Sin(a1)+2*Cos(b1));
Out> "sin(a1) + 2 * cos(b1)";
|
See also:
PrettyForm
,
TeXForm
.
Write -- Low-level printing routine
Internal function
Calling format:
Parameters:
expr - the expression to be printed
Description:
The expression "expr" is evaluated and written to the current
output. Note that Write accept an arbitrary number of arguments, all
of which are written to the current output (see second
example). Write always returns True.
Examples:
In> Write(1);
1Out> True;
In> Write(1,2);
1 2Out> True;
|
Write does not write a newline, so the Out> prompt
immediately follows the output of Write.
See also:
Echo
,
WriteString
.
WriteString -- Low-level printing routine for strings
Internal function
Calling format:
Parameters:
string - the string to be printed
Description:
The expression "string" is evaluated and written to the current
output without quotation marks. The argument should be a
string. WriteString always returns True.
Examples:
In> Write("Hello, world!");
"Hello, world!"Out> True;
In> WriteString("Hello, world!");
Hello, world!Out> True;
|
This example clearly shows the difference between Write and
WriteString. Note that Write and WriteString do not write a newline,
so the Out> prompt immediately follows the output.
See also:
Echo
,
Write
.
Space -- Print one or more spaces
Standard library
Calling format:
Parameters:
nr - the number of spaces to print
Description:
The command Space() prints one space on the
current output. The second form prints nr spaces on the current
output. The result is always True.
Examples:
See also:
Echo
,
Write
,
NewLine
.
NewLine -- Print one or more newline characters
Standard library
Calling format:
Parameters:
nr - the number of newlines to print
Description:
The command NewLine() prints one newline character
on the current output. The second form prints "nr" newlines on the
current output. The result is always True.
Examples:
In> NewLine();
Out> True;
|
See also:
Echo
,
Write
,
Space
.
FromFile -- Connect current input to a file
Internal function
Calling format:
Parameters:
name - the name of the file to read
body - the command to be executed
Description:
The current input is connected to the file "name". Then the command
"body" is executed. Everything that the commands in "body" read
from current input, is now read from the file "name". Finally, the
file is closed and the result of evaluating "body" is returned.
Examples:
Suppose that the file foo contains
Then we can have the following dialogue:
In> FromFile("foo") res := Read();
Out> 2+5;
In> FromFile("foo") res := ReadToken();
Out> 2;
|
See also:
ToFile
,
FromString
,
Read
,
ReadToken
.
FromString -- Connect current input to a string
Internal function
Calling format:
Parameters:
str - a string containing the text to parse
body - the command to be executed
Description:
The commands in "body" are executed, but everything that is read
from the current input is now read from the string "str". The
result of "body" is returned.
Examples:
In> FromString("2+5; this is never read") \
res := Read();
Out> 2+5;
In> FromString("2+5; this is never read") \
res := Eval(Read());
Out> 7;
|
See also:
ToString
,
FromFile
,
Read
,
ReadToken
.
ToFile -- Connect current output to a file
Internal function
Calling format:
Parameters:
name - the name of the file to write the result to
body - the command to be executed
Description:
The current output is connected to the file "name". Then the command
"body" is executed. Everything that the commands in "body" print
to the current output, ends up in the file "name". Finally, the
file is closed and the result of evaluating "body" is returned.
Examples:
Take first a look at the following command:
In> [ Echo("Result:"); \
PrettyForm(Taylor(x,0,9) Sin(x)); ];
Result:
3 5 7 9
x x x x
x - -- + --- - ---- + ------
6 120 5040 362880
Out> True;
|
Now suppose one wants to send the output of this command to a
file. This can be achieved as follows:
In> ToFile("out") [ Echo("Result:"); \
PrettyForm(Taylor(x,0,9) Sin(x)); ];
Out> True;
|
After this command the file out contains:
Result:
3 5 7 9
x x x x
x - -- + --- - ---- + ------
6 120 5040 362880
|
See also:
FromFile
,
ToString
,
Echo
,
Write
,
WriteString
,
PrettyForm
,
Taylor
.
ToString -- Connect current output to a string
Internal function
Calling format:
ToString() body
Parameters:
body - the command to be executed
Description:
The commands in "body" are executed. Everything that is printed on
the current output, by Echo for instance, is
collected in a string and this string is returned.
Examples:
In> str := ToString() [ WriteString( \
"The square of 8 is "); Write(8^2); ];
Out> "The square of 8 is 64";
|
See also:
FromFile
,
ToString
,
Echo
,
Write
,
WriteString
.
Read -- Read an expression from current input
Internal function
Calling format:
Read()
Parameters:
none
Description:
Read an expression from the current input, and return it unevaluated. When
the end of an input file is encountered, the token atom EndOfFile is returned.
Examples:
In> FromString("2+5;") Read();
Out> 2+5;
In> FromString("") Read();
Out> EndOfFile;
|
See also:
FromFile
,
FromString
,
LispRead
,
ReadToken
,
Write
.
LispRead -- Read an expression in LISP-syntax
Internal function
Calling format:
LispRead()
Parameters:
none
Description:
Read an expression in LISP syntax from the current input, and return
it unevaluated. When the end of an input file is encountered, the
token atom EndOfFile is returned.
The expression a+b is written in LISP syntax as (+ a b). The advantage of this syntax is that it is
less ambiguous than the infix operator grammar that Yacas uses by
default.
Examples:
In> FromString("(+ a b)") LispRead();
Out> a+b;
In> FromString("(List (Sin x) (- (Cos x)))") \
LispRead();
Out> {Sin(x),-Cos(x)};
|
See also:
FromFile
,
FromString
,
Read
,
ReadToken
,
FullForm
.
ReadToken -- Read an token from current input
Internal function
Calling format:
ReadToken()
Parameters:
none
Description:
Read a token from the current input, and return it unevaluated. When
the end of an input file is encountered, the token atom EndOfFile is returned.
A token is for computer languages what a word is for human languages:
it is the smallest unit in which a command can be divided, so that the
semantics (that is the meaning) of the command is in some sense a
combination of the semantics of the tokens. Hence a := foo consists of three tokens, namely a, :=, and foo.
Examples:
In> FromString("a := Sin(x)") While \
((tok := ReadToken()) != EndOfFile) \
Echo(tok);
a
:=
Sin
(
x
)
Out> True;
|
See also:
FromFile
,
FromString
,
Read
,
LispRead
.
Load -- Evaluate all expressions in a file
Internal function
Calling format:
Load(name)
Parameters:
name - name of the file to load
Description:
The file "name" is opened. All expressions in the file are read and
evaluated. Load always returns true.
See also:
Use
,
DefLoad
,
DefaultDirectory
,
FindFile
.
Use -- Load a file, but not twice
Internal function
Calling format:
Use(name)
Parameters:
name - name of the file to load
Description:
If the file "name" has been loaded before, either by an earlier call
to Use or via the DefLoad
mechanism, nothing happens. Otherwise all expressions in the file are
read and evaluated. Use always returns true.
The purpose of this function is to make sure that the file will at
least have been loaded, but is not loaded twice.
See also:
Load
,
DefLoad
,
DefaultDirectory
.
DefLoad -- Load a .def file
Internal function
Calling format:
DefLoad(name)
Parameters:
name - name of the file (without .def suffix)
Description:
The suffix .def is appended to "name" and the
file with this name is loaded. It should contain a list of functions,
terminated by a closing brace \} (the end-of-list delimiter). This
tells the system to load the file "name" as soon as the user calls
one of the functions named in the file (if not done so already). This
allows for faster startup times, since not all of the rules databases
need to be loaded, just the descriptions on which files to load for
which functions.
See also:
Load
,
Use
,
DefaultDirectory
.
FindFile -- Find a file in the current path
Internal function
Calling format:
Parameters:
name - name of the file or directory to find
Description:
The result of this command is the full path to the file that would be
opened when the command Load(name) would be
invoked. This means that the input directories are subsequently
searched for a file called "name". If such a file is not found, FindFile returns an empty string.
FindFile("") returns the name of the default directory (the first one on the search path).
See also:
Load
,
DefaultDirectory
.
PatchLoad -- Execute commands between <? and ?> in file
Internal function
Calling format:
Parameters:
name - the file to patch
Description:
PatchLoad loads in a file and outputs the contents to the current
output. The file can contain blocks delimited by <? and ?>
(meaning Yacas Begin and Yacas End). The piece of text between
such delimiters is treated as a separate file with Yacas instructions,
which is then loaded and executed. All output of write statements
in that block will be written to the same current output.
This is similar to the way php works. You can have a static text file
with dynamic content generated by Yacas.
See also:
PatchString
,
Load
.
Nl -- A newline character
Standard library
Calling format:
Description:
This function returns a string with one element in it, namely a newline
character. This may be useful for building strings to send to some
output in the end.
Note that the second letter in the name of this command is a lower
case L (from "line").
Examples:
In> WriteString("First line" : Nl() : "Second line" : Nl());
First line
Second line
Out> True;
|
See also:
NewLine
.
V -- Verbose mode output
Standard library
Calling format:
Parameters:
expression - expression to be evaluated in verbose mode
Description:
The function V(expression) will evaluate the expression in
verbose mode. Various parts of Yacas can show extra information
about the work done while doing a calculation when using V.
Examples:
In> Solve({x+2==0},{x})
Out> {{-2}};
In> V(Solve({x+2==0},{x}))
Entering Solve
From x+2==0 it follows that x = -2
x+2==0 simplifies to True
Leaving Solve
Out> {{-2}};
|
See also:
Echo
,
N
,
Solve
.